Referring to FIG. 1, there is shown a lateral sectional view of a conventional color cathode ray tube (CRT) 10. The sectional view of FIG. 1 is taken down a vertical center-line through CRT 10 such that only elements of the CRT's center electron gun 11 are shown in the figure, it being understood that in an inline color CRT an outer electron gun is disposed on each side of the center electron gun. The electron guns are disposed within a sealed glass envelope 28 having a generally cylindrical neck portion 28a, a frusto-conical funnel portion 28b, and a display screen 14. Disposed in a sealed manner on an aft portion of the glass envelope's neck portion 28a is a plug-like connector 31 comprised of a plastic housing and a plurality of conductive pins 32 extending in a sealed manner from a distal end of the glass envelope's neck portion 28a. The combination of connector 31 and pins 32 is adapted for insertion in a socket for providing power and control signals to CRT 10. Disposed on an inner surface of display screen 14 is a phosphor layer 16 responsive to an electron beam incident thereon for providing a video image. The phosphor layer 16 is in the form of a large number of discrete phosphor elements arranged in groups of three for each of the primary colors, i.e., red, green and blue. A charged metal shadow mask 42 having a large number of apertures therein is disposed immediately adjacent to the phosphor layer 16. Each of the apertures in shadow mask 42 is aligned with a respective one of the aforementioned phosphor elements in phosphor layer 16 for allowing an electron beam to be incident upon the phosphor element as the electron beams are swept across the inner surface of display screen 14 in a raster-like manner. The charged shadow mask 42 serves as a color selection electrode, ensuring that each of the three electron beams lands only on its assigned phosphor elements, or deposits.
The multi-electrode electron gun 11 includes, in proceeding toward display screen 14, a low voltage beam forming region (BFR) 34, a symmetric prefocus lens 36 and a high voltage main focus lens 38. Energetic electrons are emitted by a plurality of heated cathodes K (only one of which is shown in the figure for simplicity) in the general direction of display screen 14. BFR 34 is aligned with cathodes K to receive the energetic electrons and form these electrons into a beam along an axis A--A', it being understood that outer electron beams are similarly formed on each side of the center electron beam 12 shown in dotted-line form. BFR 34 typically includes a G.sub.1 electrode, a G.sub.2 electrode, and a facing portion of a G.sub.3 electrode. Electron beam 12 is then directed to the symmetric prefocus lens 36 which typically includes a G.sub.4 electrode and facing portions of the G.sub.3 electrode and a G.sub.5 electrode. From the symmetric prefocus lens 36, the beam passes through a main focus lens 38 comprised of a G.sub.6 electrode and a facing portion of the G.sub. 5 electrode. The main focus lens 38 focuses the electron beam 12 on the inner surface of display screen 14. Disposed about and engaging the G.sub.6 electrode is a support, or convergence, cup 20. Attached to support cup 20 about its outer periphery are a plurality of contact clips, or bulb spacers, 22 which engage an adjacent inner surface of the neck portion 28a of the CRT's glass envelope 28. Support cup 20 provides support for the G.sub.6 electrode and maintains electron gun 11 securely in position in the neck portion 28a of the CRT's glass envelope 28. Each of the aforementioned electrodes is coupled to and supported by glass beads (also not shown for simplicity) disposed in the glass envelope's neck portion 28a.
After being focused by the lens arrangement of electron gun 11, electron beam 12 passes through a magnetic deflection yoke 18 disposed about the frusto-conical funnel portion 28b of the CRT's glass envelope 28. A conductive layer (not shown) on the inner surface of the CRT's glass envelope 28 is electrically coupled to an anode button 30 extending through the CRT's glass envelope 28 and which, in turn, is coupled to an anode voltage V.sub.A source (which also is not shown in the figure for simplicity). The G.sub.6 grid is generally comprised of a material exhibiting high magnetic permeability to shield the electron beams within the CRT's main focus lens 38 from the magnetic deflection field of yoke 18. The prior art therefore teaches the separation of the beam's electrostatic focus field and the magnetic deflection field.
The electron gun's main focus lens 38 is therefore typically comprised of the G.sub.5 and G.sub.6 electrodes and has a focal point 26 located on the electron beam axis A--A' generally intermediate these two charged electrodes. The main focus lens 38 formed of electrodes G.sub.5 and G.sub.6 also has an equivalent lens size, which is relatively small in diameter, for the typical electron gun 11 shown in FIG. 1 because of the relatively small diameter of these focus electrodes. Deflection yoke 18 typically is comprised of a ferrite core about which is wound two sets of current carrying conductors for establishing a timevarying magnetic field within the CRT 10 for deflecting electron beam 12 across the inner surface of the display screen 14 in a raster-like manner. In a conventional CRT, the electron beam is therefore first electrostatically focused and then magnetically deflected across the display screen 14. A beam deflection center is formed in a magnetic deflection region 40 such as on a deflection center axis D--D' shown in FIG. 1, with its location depending upon the size and shape of the core and conductive wire arrangement in the deflection yoke 18. As shown in the figure, the main focus lens 38 is displaced from the magnetic deflection region and the deflection center line D--D'. This spatial separation of the CRT's focus and deflection regions is one factor which establishes the CRT's length.
One problem with the prior art CRT 10 shown in FIG. 1 arises from the sequential focusing and deflection of the electron beams. For example, when the center electron beam 12 reaches the deflection center line D--D', the electrons have been accelerated to a high energy by the anode voltage V.sub.A which is applied to the G.sub.6 electrode and is typically on the order of 25 kV. Because the amount of deflection for a given magnetic field is inversely proportional to the square root of electron beam voltage a large magnetic field is required to deflect the beam. This generally requires a larger deflection yoke and/or increased current in the yoke windings which gives rise to thermal dissipation problems and requires a larger yoke power supply. Therefore, prior art CRTs suffer from limited electron beam deflection sensitivity. High deflection sensitivity for the electron beam is particularly important in the current high resolution CRTs with higher deflection frequencies. In order to accommodate these faster deflection rates, Litz wire in the form of a bundle of twisted wires is frequently used to provide a greater surface area in taking advantage of the increased skin effect of these types of conductors. Unfortunately, Litz wires are substantially more expensive than a strand of conventional copper wire and of limited commercial value in consumer-type CRTs.
The present invention addresses the aforementioned limitations of the prior art by providing a deflection lens for a multi-beam electron gun in a color CRT which allows for simultaneous and co-located focusing and deflection of the CRT's electron beams. By deflecting the beam in a lower voltage region and positioning the electron beam deflection center within the focal point of the CRT's main focus lens, increased beam deflection sensitivity is realized, the length of the CRT as well as the diameter of its neck portion may be reduced, and lens magnification, electron beam space charge effect and lens spherical aberration are reduced for improved video image quality.